The present invention relates to an instrument for treating a sample solution to be supplied to a biosensor for analysis and a method for treating a sample solution using the same. More specifically, the present invention relates to a sample treating kit and a sample treating method using the same for analysis with a biosensor.
One method for simple quantitative measurement of a specific component contained in a sample solution is to determine oxidation current by reacting, in the presence of an electron acceptor, the specific component with an oxidoreductase corresponding to the substrate of the specific component and electrochemically oxidizing the reduced electron acceptor.
Biosensors using this measurement principle enable measurement of various substances if a proper oxidoreductase corresponding to the substrate of an analyte is selected.
However, since such biosensor makes analysis with the aid of enzyme reaction and electrode reaction, smooth progress of the enzyme reaction and electrode reaction is mandatory in order to improve measurement accuracy of the biosensor.
Therefore, there are several studies to enhance enzyme activity by adjusting temperature and pH of the sample solution or remove any interfering substance with the enzyme or electrode reaction.
Moreover, sample solutions may sometimes include oxidizable substances which may produce oxidation current due to their concurrent oxidation with the electron acceptor and generate a positive error in the measured oxidation current. This can result in impaired measurement accuracy of the biosensor. Therefore, reduction of adverse effects of such oxidizable substance to a minimum becomes a requisite.
Conventional biosensors are installed with means for solving the above-mentioned problems inside their measurement system.
Here, the operation of measurement of a flow injection analyzer (YSI MODEL 2700 SELECT, made by Yellow Spring Instrument Co., Inc.) as a biosensor using an immobilized enzyme membrane and electrode reaction will be described as one example.
The measurement system of this analyzer comprises an electrode system including at least a working electrode and a counter electrode, an immobilized enzyme membrane attached to the electrode system, a sample chamber to which a sample solution is supplied to make measurement there, and an electric circuitry connected to the electrode system.
First, one end of an aspiration tube for aspirating a sample whose other end communicates with the sample chamber is immersed in a sample solution and the solution is aspirated by the tube and supplied to the sample chamber through the communicating other end. At that time, a certain amount of buffer solution is aspirated by another aspiration tube and supplied to the sample chamber.
Subsequently, the sample solution and the buffer solution thus supplied are mixed by agitation using a stirrer installed in the sample chamber. When a certain time has passed after supply of the sample solution and buffer solution, electrochemical measurement is performed to quantitate the analyte in the sample solution.
Any analyzer having such structure adjusts pH of the sample solution to a suited pH for enzyme reaction and dilutes the sample solution to an appropriate concentration by supplying the buffer solution to the sample chamber.
Concurrent agitation of the sample solution and buffer solution facilitates their rapid mixing on one hand and promotes dissolution of the enzyme in the mixed solution on the other hand. This in turn enables supply of sufficient oxygen to proceed enzyme reaction.
Despite the above advantages, such analyzer requires exchange of the immobilized enzyme membrane with a proper one depending on the analyte. Moreover, since the pH range proper for enzyme reaction varies by enzyme, the buffer solution must be exchanged concurrently. This renders manipulation of the analyzer inconvenient.
Although dilution of the sample solution reduces adverse effects of the interfering substances hindering enzyme and electrode reactions and the oxidizable substance, complete elimination of these effects is much difficult. This limits the extent of improvement of the measurement accuracy.